The Pakistan government has deployed 4,000 troops in the Swat valley of North West Frontier Province to counter the activities of a pro-Taliban cleric whose men have challenged the writ of the local administration.

The move came hours after four security personnel were injured in a bomb attack on a military caravan in the Malakand area late on Tuesday. Seven persons were arrested in connection with the attack.

Military spokesman Maj Gen Waheed Arshad on Wednesday said the paramilitary troops had been deployed to stop the illegal activities of Maulana Faizullah, a radical cleric who is popularly known as the "FM Maulana" for his fiery sermons and edicts broadcast on an illegal FM radio station.

Faizullah is the leader of the band Tanzim Nifaz-e-Shariat Muhammadi and has thousands of followers.

Reports from Swat, located 50 km from the provincial capital of Peshawar, said the troops were advancing towards Faizullah's madrassa. Many people were fleeing the region as they were apprehensive about the outbreak of violent clashes.

Local residents said helicopter gunships were hovering over the region and troops had closed many roads and entry points to the Swat region, which till recently was popular with tourists. All schools in the area have also been closed.

The drive against Faizullah is part of a larger operation by the NWFP government to curb militant activities in the region. The army has decided to act against the cleric in the first phase as he is the most influential militant leader in the area, sources said.

The Frontier Corps troops are setting up check posts across the Swat region and will work with local police to aid the civil administration to stop Faizullah and his men "terrorising" the people, Arshad said.

"The posts have been set up to protect the people. All steps will be taken to stop the activities of Faizullah and his band of criminals," he said.

Arshad warned strong action would be taken against the militants if they did not turn themselves in to the authorities.

Dawn's News channel quoted sources close to Faizullah as saying that he welcomed the deployment of the troops.

The sources also said Faizullah would cooperate with the law enforcement agencies to restore peace in the area bordering the restive tribal region that have recently witnessed violent clashes between troops and pro-Taliban militants.

In recent months, Faizullah has called for a jihad in his FM broadcasts. He had recently said he would impose an Islamic tax for the "protection" provided by his armed men to the local people.

Faizullah's men have also been challenging the local administration and carrying out attacks on security personnel.

His men have even taken over traffic control duties and the cleric had stepped up his calls for a jihad since the siege of the Lal Masjid in Islamabad.

The Pakistan Army had earlier sent troops into Swat in July as part of an operation against militancy in the region, but this triggered bombings and suicide attacks by the rebels.